Copyright © 2009 John Wiley & Sons, Ltd and ERP Environment * Correspondence to: M. Haasnoot, Deltares, PO Box 177, 2600 MH Delft, The Netherlands. E-mail: marjolijn.haasnoot@deltares.nl Sustainable Development Sust. Dev. (2009) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/sd.438 A Method to Develop Sustainable Water Management Strategies for an Uncertain Future M. Haasnoot, 1,2,3 * H. Middelkoop, 1 E. van Beek 2,3 and W. P. A. van Deursen 4 1 Utrecht University, Department of Physical Geography, Utrecht, The Netherlands 2 Deltares, Delft, The Netherlands 3 University of Twente, Department of Water Engineering and Management, Enschede, The Netherlands 4 Carthago Consultancy, Rotterdam, The Netherlands ABSTRACT Development of sustainable water management strategies involves identification of vulner- ability and adaptation possibilities, followed by an effect analysis of these adaptation strat- egies under different possible futures. Recent scenario studies on water management were mainly ‘what-if’ assessments in one or two future situations. The future is, however, more complex and dynamic. It involves general trends and unexpected events in both the water and the social system. Moreover, the two systems interact: society responds to events and the state of the water system changes in response to management. In this paper we discuss a transdisciplinary approach. Key elements in the concept are (1) the model of pressure, state, impact and response, (2) the Perspectives method to consider uncertainties of social and natural systems and (3) the evaluation of the system using transient scenarios in which we consider time series of trends, events and interaction between the water system and society. The effect analysis is executed with an integrated assessment meta-model based on simple cause–effect relations and response curves. Copyright © 2009 John Wiley & Sons, Ltd and ERP Environment. Received 21 August 2009; accepted 21 September 2009 Keywords: sustainable water management; climate change; uncertainty; transient scenarios Introduction W ATER MANAGEMENT GENERALLY AIMS AT PROVIDING ADEQUATE AMOUNTS OF WATER OF PROPER QUALITY FOR the various water-related services. Particularly in developed societies, water systems have been mod- ified or trained to fulfil the demands of the water services in the longer term. Failure of the water system functioning, as in the case of flood disasters, water shortage or severe pollution, has led in many cases to adaptation of the water system. Examples are dike enforcement, river regulation and reservoir build- ing, or the establishment of wastewater treatment plants. In recent years, extreme floods, the need for ecological rehabilitation of rivers and the prospect of future global change has raised the awareness that new water manage- ment strategies might be needed over the forthcoming years to ensure sustainable use of the water system over